U.S. patent number 5,549,738 [Application Number 08/237,693] was granted by the patent office on 1996-08-27 for platinum electroforming bath.
This patent grant is currently assigned to Electroplating Engineers of Japan, Limited. Invention is credited to Katsutsugu Kitada, Soumei Yarita.
United States Patent |
5,549,738 |
Kitada , et al. |
August 27, 1996 |
Platinum electroforming bath
Abstract
The invention relates to platinum electroforming and platinum
electroplating capable of preparing a deposited platinum material
having high hardness and increased thickness and size. The platinum
electroforming or electroplating bath comprises at least one
compound selected from the group consisting of chloroplatinic acid,
chloroplatinates of alkali metals, hydrogen hexahydroxoplatinate,
and hexahydroxoplatinates of alkali metals, 2-100 g/l as platinum
and a hydroxylated alkali metal, 20-100 g/l.
Inventors: |
Kitada; Katsutsugu
(Kanagawa-ken, JP), Yarita; Soumei (Kanagawa-ken,
JP) |
Assignee: |
Electroplating Engineers of Japan,
Limited (JP)
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Family
ID: |
27527037 |
Appl.
No.: |
08/237,693 |
Filed: |
May 4, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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718767 |
Jun 21, 1991 |
5310475 |
May 10, 1994 |
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Foreign Application Priority Data
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Jun 29, 1990 [JP] |
|
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2-170064 |
Jul 16, 1990 [JP] |
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2-185241 |
Apr 30, 1991 [JP] |
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3-124577 |
Apr 30, 1991 [JP] |
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3-124578 |
Apr 30, 1991 [JP] |
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3-124579 |
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Current U.S.
Class: |
106/1.21;
205/264 |
Current CPC
Class: |
A44C
27/002 (20130101); C25D 3/567 (20130101); C25D
3/50 (20130101) |
Current International
Class: |
A44C
27/00 (20060101); C25D 3/56 (20060101); C25D
3/50 (20060101); C25D 3/02 (20060101); C25D
003/52 () |
Field of
Search: |
;205/264 ;106/1.21 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Davies et al, "Platinum Plating from Alkaline Solutions", Intern.
Electrodep. Conf., 1937, advance copy. .
Indira et al, "Addition Agent for Platinum Plating", Metal
Finishing, May 1969, pp. 44-49..
|
Primary Examiner: Niebling; John
Assistant Examiner: Mayekar; Kishor
Attorney, Agent or Firm: Klauber & Jackson
Parent Case Text
RELATED APPLICATIONS
This application is a continuation of application Ser. No.
07/718,767, filed Jun. 21, 1991, now U.S. Pat. No. 5,310,475, to be
issued May 10, 1994.
Claims
What is claimed is:
1. A platinum electroforming bath consisting of a
hexahydroxyplatinate of hydrogen or an alkali metal, present in an
amount of 2-100 g/l; an alkali metal hydroxide, present in an
amount of 20-100 g/l; and an alkali metal carboxylate, present, in
an amount of 20-100 g/l.
2. The platinum electroforming bath of claim 1 consisting of
H.sub.2 Pt(OH).sub.6, KOH and K.sub.2 C.sub.2 O.sub.4.H.sub.2 O.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a platinum electroforming and also
to a platinum electroplating.
Platinum has widely been used as ornaments or accessories because
of its clean and subdued shine, although it has a less loud color
than gold. Platinum is also highly resistant to corrosion and gives
a catalytic effect, and thus it can be adopted as materials for
products used in industries.
Platinum, however, has an inherent tenacity, which brings about a
decreased workability of platinum. A high degree of technical skill
of a professional workman is imperative especially for the working
of accessories such as earrings or brooches which requires
elaborate workmanship for the manufacture.
Furthermore, inasmuch as the specific gravity of platinum is
higher, for example, than that of white gold made of an alloy of
gold and silver, it cannot be made into a large-sized accessories
as put on a personal body. There have been limitations on the size
of such commercial platinum products.
For these reasons, the present inventor has undertaken studies
pertinent to a platinum electroforming method to solve the
above-mentioned problems i.e., the limitations on workability and
size. Specifically, these studies have been directed to a method
including the stages of forming by means of electrodeposition a
thick deposition layer of platinum on the surface of a mother die
to which a release coat has been applied and releasing the
deposited layer from the mother die to obtain an electroformed
product of platinum having opposite convex and concave surfaces to
those of the mother die. Adding to these stages the method may
include the stages of applying a release coat to the surface of the
resultant electroformed product and treating by means of
electrodeposition to obtain a product of platinum having the same
convex and concave surfaces as those of the mother die. If the
electroforming method may be materialized, it may simultaneously
solve the problems such as the deficient workability and the
limitation on size of platinum as aforementioned since it allows to
conveniently prepare hollow products of platinum or products with a
film of any thickness of platinum.
2. Description of the Prior Art
From the above reasons, there has been a great demand for the
electroforming of platinum. In fact, various studies on the
electroforming of platinum have been conducted. However, no
successful process has been completed so far.
This is because a thickness of a deposited layer to be required in
the electroforming is about 10-50 times as large as usual
electroplating (for example, Japanese Patent Laid-open Publication
No. 107,794/1990). Specifically, one will fail to prepare the
deposited layer of such a thickness because deposited platinum has
a tendency to occlude hydrogen, which increases an internal stress
of the deposited layer, resulting in generation of cracks (micro
crevices). Thus, one can not obtain the desirable deposited layer
having sufficient strength and thickness to be used for commercial
products. In particular, special consideration must be given to
physical and mechanical properties of the deposited layer, since
the deposited layer per se becomes a product of electroforming. The
generation of cracks may therefore cause fatal problems to the
electroformed products.
In addition, a general platinum metal, which is not a deposited
metal prepared by electroforming or electroplating, has a crystal
structure of face centered cubic lattice. Also, it is soft
(approximately 40 Hv) and ductile. However, ornaments, e.g. rings,
necklaces made of platinum having these characteristics possess the
drawbacks of being easily scratched and deformed because they are
soft and abradable.
Because of these reasons, platinum is conventionally alloyed with
other metals to increase hardness for manufacturing ornaments using
platinum. This method, though it allows the hardness of the
platinum alloy to increase, however, causes generation of
intermetallic compounds in the platinum alloy to result in
brittleness of the platinum alloy. The method has also the
disadvantage of generation of an oxide film in the steps of heating
or brazing a platinum alloy, thereby reducing the external quality
of the platinum alloy.
In view of this situation, it has been desired to develop means
other than these alloying methods to improve the hardness of a
platinum alloy.
SUMMARY OF THE INVENTION
One of the objects of the present invention is to provide a
platinum electroforming bath capable of producing a platinum
deposit having a considerable strength and thickness.
It is another object of the present invention to provide a method
for preparing a platinum material having high hardness by adopting
electrodeposition from a platinum electrolytic bath (platinum
electroforming or electroplating bath) as means for improving the
hardness of platinum.
Other objects, features and advantages of the invention will
hereinafter become more readily apparent from the following
description.
DESCRIPTION OF PREFERRED EMBODIMENTS
The platinum electroforming or plating bath according to the
present invention comprises:
at least one compound selected from the group consisting of
chloroplatinic acid, chloroplatinates of alkali metals, hydrogen
hexahydroxoplatinate, and hexahydroxoplatinates of alkali metals,
2-100 g/l as platinum; and
a hydroxylated alkali metal, 20-100 g/l.
As a salt of platinum, chloroplatinic acid [H.sub.2 PtCl.sub.6 ] or
hydrogen hexahydroxoplatinate [H.sub.2 Pt(OH).sub.6 ] is
preferable. Their salts of alkali metals are also preferable. Among
these salts, sodium chloroplatinate [Na.sub.2 PtCl.sub.6 ],
potassium chloroplatinate [K.sub.2 PtCl.sub.6 ], and the like are
preferable as the chloroplatinate of alkali metals, and sodium
hexahydroxoplatinate [Na.sub.2 Pt(OH).sub.6.2H.sub.2 O], potassium
hexahydroxoplatinate [K.sub.2 Pt(OH).sub.6 ], and the like are
preferable as the hexahydroxoplatinate of alkali metals. A
preferable amount of these platinum salts to be incorporated is
2-100 g/l as platinum.
Preferable examples of the hydroxylated alkali metals are potassium
hydroxide and sodium hydroxide. The hydroxylated alkali metal is
incorporated in order to dissolve platinum, preferably, in an
amount of 20-100 g/l.
Given as examples of preferable soluble carboxylate are potassium
or sodium salts of acetic acid, oxalic acid, citric acid, malic
acid, propionic acid, lactic acid, malonic acid, tartaric acid, and
the like. Preferable examples of the phosphate are potassium
phosphate, sodium phosphate, dipotassium hydrogenphosphate,
disodium hydrogenphosphate, potassium hydrogenphosphate, sodium
hydrogenphosphate, and the like. As the sulfate, potassium sulfate,
sodium sulfate, and the like are preferable.
Such a soluble calboxylate or the like acts as a stabilizer in the
electroforming or plating bath. It is preferably incorporated in an
amount of 2-200 g/l.
In addition to the above components, the electroforming or plating
bath of platinum may include additives such as various brightening
agents, electroconductive salts, and the like.
Additionally, a platinum alloy can be deposited by incorporating
other metal salts in the electroforming or plating bath. Preferable
examples of metals adapted to make an alloy with platinum are gold,
silver, palladium, iridium, ruthenium, cobalt, nickel, copper, and
the like. The number of other metals being incorporated is not
restricted to one. Two kinds of metals can be incorporated to make
an alloy with platinum, for example, an alloy of
platinum-palladium-copper.
A preferable operating temperature for the electroforming or
plating bath is not lower than 65.degree. C., with the temperature
of not lower than 80.degree. C. being particularly preferable.
Generally, a current density is preferably 1-3 ASD, when platinum
is contained in the amount of 20 g/l, though it depends on plating
conditions.
A platinum metal produced by means of electrodeposition from the
platinum electrolytic bath has a reduced crystal size. The platinum
metal has also a hardness of at least 100-350 Hv. Such hardness is
greatly higher than that of a platinum metal, i.e. about 40 Hv,
prepared by general melting procedures.
There is the following relationship between the purity and hardness
of the platinum material prepared by the method of the present
invention:
______________________________________ Purity (wt %) Hardness
______________________________________ 99.9 Above 100 H.sub.v
95.0-99.9 Above 200 H.sub.v 90.0-95.0 Above 250 H.sub.v 85.0-90.0
Above 300 H.sub.v ______________________________________
Microscopic and macroscopic stresses are involved in the platinum
metal obtained by means of electrodeposition. The microscopic
stress which is a non-uniformed stress corresponding to an expanded
width of X-ray diffraction lines causes the increased hardness of
the deposited metal. While the macroscopic stress is a residual
tensile or compressive stress involved in the deposited platinum
metal and makes a cause of strain or cracks. The macroscopic stress
of platinum is very large. The macroscopic stress, however, can be
restrained by adopting an alkaline platinum electrolytic bath or by
annealing (heat treatment) for each additional thickness of about
5-10 .mu.m of a deposited layer. The annealing is performed under
heating, preferably, at 400.degree.-900.degree. C. for 30-120 min.
By the annealing, the hardness of the platinum metal may be
reduced. Such degree of the reduced hardness is nevertheless higher
than that of conventional platinum metals. Accordingly, the
deposited layer having sufficiently large thickness and size can be
provided, and thus platinum products having high hardness can be
manufactured by means of, namely, the electroforming.
As a platinum electrolytic bath when adopting a means of platinum
electroforming or electroplating to improve the hardness of
platinum, an alkaline bath is very advantageous from the aspect of
deposition efficiency, a macroscopic stress, and the like. In this
respect, the platinum electrolytic bath includes one or more
platinum compounds selected from the group consisting of
tetrachloroplatinate, hexachloroplatinate, tetrabromoplatinate,
hexabromoplatinate, hexahydroxoplatinate, diamminedinitroplatinum,
tetranitroplatinate, and the like; and one or more compounds
selected from the group consisting of hydroxylated alkali metals,
ammonia, conductive salts, and the like, and, as required, may
include alloying metal salts.
Stated additionally, the annealing is not necessary when using as
the platinum electrolytic bath the previously mentioned composition
comprising:
at least one compound selected from the group consisting of
chloroplatinic acid, chloroplatinates of alkali metals, hydrogen
hexahydroxoplatinate, and hexahydroxoplatinates of alkali metals,
2-100 g/l as platinum; and
a hydroxylated alkali metal, 20-100 g/l.
Other features of the invention will become apparent in the course
of the following description of the exemplary embodiments which are
given for illustration of the invention and are not intended to be
limiting thereof.
EXAMPLES
Example 1
A preferable example of the electroforming of the present invention
is herein illustrated.
TABLE 1 ______________________________________ (Composition of a
platinum electroforming bath)
______________________________________ Hydrogen
hexahydroxoplatinate 30 g/l [H.sub.2 Pt(OH).sub.6 ] Potassium
acetate 40 g/l [KCH.sub.3 CO.sub.2 ] Potassium hydroxide 60 g/l
[KOH] ______________________________________ pH: 13.5
A test was performed using the above electroforming bath shown in
Table 1 under the different conditions with respect to the time and
the current density to deposit a deposition layer of platinum on
the surface of a test piece of brass.
The results are shown in Table 2. The deposition layers obtained
all exhibited an excellently glossy appearance. Observation under
microscope showed no existence of cracks. Further, the deposition
layers had an increased thickness in proportion to the
electroforming time. These results demonstrate that the bath can be
used as an electroforming bath. Accordingly, light and large-sized
earrings or brooches with a hollow construction can be produced by
the method using the electroforming bath of the present invention.
Also, elaborate works can be achieved without using high technical
skill.
TABLE 2 ______________________________________ Electro- Current
Deposition Thickness of Forming Density Efficiency Deposition No.
min ASD mg/A .multidot. min .mu.m
______________________________________ 1 4 3 29.3 1.64 2 4 3 29.6
1.66 3 60 3 29.6 24.8 4 153 2 29.2 41.7 5 240 2 29.3 65.6 6 265 2
29.5 72.9 7 180 3 29.4 74.0 8 480 2.3 29.5 150
______________________________________
Example 2
In this example, an experiment of producing an insoluble platinum
electrode was performed by plating platinum on titanium. A plating
bath having the same composition as that of the electroforming bath
shown in Table 1 was used in this example. The plating was carried
out using this plating bath under the following operating
conditions.
Plating method: dip plating
Bath temperature: 80.degree. C.
Current density: 3 ASD
Plating time: 10 min
Inspection of the insoluble platinum electrode obtained revealed
that an adhesive platinum layer having a glossy surface with a
thickness of 4 .mu.m was formed. The surface of the platinum layer
was observed under a microscope to show that any pin hole or crack
did not occur. It was confirmed that a uniform current distribution
could be obtained when this insoluble platinum electrode was used
as an electrode in practice and also that the platinum layer on the
surface of the electrode was never peeled off from titanium which
was a metal underneath over a prolonged period of time.
The platinum plating according to the present invention, however,
is not restricted to use in a field of the above insoluble platinum
electrode, but can be applied to, for example, the formation of a
platinum layer on a heat resisting section of a jet turbine.
Example 3
Electroforming was carried out using the electrolytic baths No.
1-11 having the compositions and conditions as tabulated below to
deposit platinum on a test piece of brass, while deposited layers
were annealed during the above procedures when their microscopic
stresses were high. The deposited layers (platinum material)
obtained had high hardness, the surface thereof being smooth. Also,
the flexibility of the deposited layer stood comparison with that
of ordinary platinum.
Electrolytic Bath No.1
______________________________________ Composition Pt [as
Pt(NH.sub.3).sub.2 (NO.sub.2).sub.2 ] 10 g/l C.sub.5 H.sub.5 N 200
ml/l NH.sub.3 100 ml/l Condition pH 13 (adjusted by NaOH)
Temperature 75.degree. C. Current density 1.0 A/dm.sup.2 Deposition
efficiency 45 mg/A .multidot. min Electrolytic time 240 min
Deposited layer Thickness 48 .mu.m Purity 99.95 wt % Hardness 270
H.sub.v ______________________________________
Electrolytic Bath No.2
______________________________________ Composition Pt [as
Pt(NH.sub.3).sub.2 (NO.sub.2).sub.2 ] 10 g/l C.sub.5 H.sub.5 N 200
ml/l NH.sub.3 100 ml/l CuSO.sub.4.5H.sub.2 O 1.97 g/l Condition pH
11 Temperature 65.degree. C. Current density 1.0 A/dm.sup.2
Deposition efficiency 30.4 mg/A .multidot. min Electrolytic time
360 min Deposited layer Thickness 48 .mu.m Purity 99.97 wt %
Hardness 330 H.sub.v ______________________________________
Electrolytic Bath No.3
______________________________________ Composition Pt [as K.sub.2
PtCl.sub.4 ] 10 g/l EDTA-2Na 80 g/l Condition pH 6 Temperature
70.degree. C. Current density 1.0 A/dm.sup.2 Deposition efficiency
10.0 mg/A .multidot. min Electrolytic time 480 min Deposited layer
Thickness 16 .mu.m Purity 99.94 wt % Hardness 283 H.sub.v
______________________________________
Electrolytic Bath No.4
______________________________________ Composition Pt [as K.sub.2
[pt(NO.sub.2).sub.4 ] 10 g/l K.sub.2 HPO.sub.3 0.5 mol/l KNO.sub.3
0.2 mol/l Condition pH 13 (adjusted by NaOH) Temperature 60.degree.
C. Current density 1.0 A/dm.sup.2 Deposition efficiency 9.4 mg/A
.multidot. min Electrolytic time 480 min Deposited layer Thickness
16 .mu.m Purity 99.97 wt % Hardness 420 H.sub.v
______________________________________
Electrolytic Bath No.5
______________________________________ Composition Pt [as H.sub.2
Pt(OH).sub.6 ] 13 g/l CH.sub.3 COONa 0.5 mol/l EDTA-4H 0.05 mol/l
NaOH 40 g/l NiSO.sub.4.6H.sub.2 O 0.04 mol/l Condition pH 13
Temperature 65.degree. C. Current density 1.0 A/dm.sup.2 Deposition
efficiency 31.0 mg/A .multidot. min Electrolytic time 360 min
Deposited layer Thickness 48 .mu.m Purity 96.2 wt % Hardness 440
H.sub.v ______________________________________
Electrolytic bath No.6
______________________________________ Composition Pt [as H.sub.2
Pt(OH).sub.6 ] 13 g/l CH.sub.3 COONa 0.5 mol/l EDTA-4H 0.05 mol/l
NaOH 40 g/l NiSO.sub.4.6H.sub.2 O 0.04 mol/l Condition pH 13
Temperature 65.degree. C. Current density 1.0 A/dm.sup.2 Deposition
efficiency 31.0 mg/A .multidot. min Electrolytic time 180 min
Deposited layer Thickness 14 .mu.m Purity 97.0 wt % Hardness 450
H.sub.v ______________________________________
Electrolytic Bath No.7
______________________________________ Composition Pt [as H.sub.2
Pt(OH).sub.6 ] 20 g/l KOH 50 g/l K.sub.2 C.sub.2 O.sub.4.H.sub.2 O
30 g/l Condition pH 13.5 Temperature 90.degree. C. Current density
3 A/dm.sup.2 Deposition efficiency 30 mg/A .multidot. min
Electrolytic time 240 min Deposited layer Thickness 100 .mu.m
Purity 99.9 wt % Hardness 350 H.sub.v
______________________________________
Electrolytic Bath No.8
______________________________________ Composition Pt [as H.sub.2
Pt(OH).sub.6 ] 20 g/l KOH 40 g/l Sn [as K.sub.2 SnO.sub.3.3H.sub.2
O] 30 g/l Potassium tartrate.1/2H.sub.2 O 100 g/l Condition pH 13.3
Temperature 90.degree. C. Current density 2 A/dm.sup.2 Deposition
efficiency 20 mg/A .multidot. min Electrolytic time 300 min
Deposited layer Thickness 60 .mu.m Purity 85 wt % Hardness 650
H.sub.v ______________________________________
Electrolytic Bath No.9
______________________________________ Composition Pt [as H.sub.2
Pt(OH).sub.6 ] 20 g/l KOH 100 g/l Zn [as ZnO] 0.8 g/l Condition pH
14 Temperature 90.degree. C. Current density 2 A/dm.sup.2
Deposition efficiency 30 mg/A .multidot. min Electrolytic time 180
min Deposited layer Thickness 50 .mu.m Purity 95 wt % Hardness 450
H.sub.v ______________________________________
Electrolytic Bath No.10
______________________________________ Composition Pt [as H.sub.2
PtCl.sub.6 ] 10 g/l C.sub.5 H.sub.5 N 200 ml/l NH.sub.3 100 ml/l
Na.sub.2 CO.sub.3 0.1 mol/l Pd 1 g/l [as cis-Pd(NH.sub.3).sub.2
(NO.sub.2).sub.2 Condition pH 12 (adjusted by NaOH) Temperature
75.degree. C. Current density 1.0 A/dm.sup.2 Deposition efficiency
32.2 mg/A .multidot. min Electrolytic time 180 min Deposited layer
Thickness 25 .mu.m Purity 85.6 wt % Hardness 505 H.sub.v
______________________________________
Electrolytic Bath No.11
______________________________________ Composition Pt (as H.sub.2
PtCl.sub.6 ] 10 g/l C.sub.5 H.sub.5 N 200 ml/l NH.sub.3 100 ml/l
Na.sub.2 CO.sub.3 0.1 mol/l Pd 1 g/l [as cis-Pd(NH.sub.3).sub.2
(NO.sub.2).sub.2 Condition pH 12 (adjusted by NaOH) Temperature
75.degree. C. Current density 1.0 A/dm.sup.2 Deposition efficiency
32.2 mg/A .multidot. min Electrolytic time 360 min Deposited layer
Thickness 49 .mu.m Purity 87.0 wt % Hardness 410 H.sub.v
______________________________________
* * * * *